Leave Me Begging Undercover
by WhiteFerrets
Summary: Sebastian is one of the most powerful and successful demons in the Underworld, but everything gets turned on its head when he falls for the witch he's been ordered to kill.


**A/N: Written for day two of Smythofsky Holidays (Supernatural AU). This is a Glee/Charmed crossover, Dave being Phoebe and Sebastian being Cole, but you don't have to be familiar with the show to read and understand this fic.**

**Rating: PG-13  
****Warning: Mentions of violence/murder, a very unhealthy relationship dynamic, and vague implications of suicide attempts.  
****Word Count: 1800  
Characters: Dave Karofsky/Sebastian Smythe.  
**

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**_I was dead before I met you._**

The deaths all begin to blur together after a while. His victims aren't really victims, not people, just faceless targets with no family and no passions and no personality to speak of. They're just a part of the job, a part of the life he was born into, the life he'll remain within until the day he dies.

He's watched their expressions change from confusion and uncertainty to fear and dread as he shifts from his human form to the one people run away from, the black patterns across his deep red skin, his teeth sharp, his nails pointed. He's heard them scream, _"Who are you? Oh my god, what are you?"_ so many times, always replying with a simple _"Belthazor."_ before sucking the life from them.

But he's not Belthazor, and this isn't living, not at all. His human half may be muted, slowly being silenced with each fireball he throws and each athame he drives into the heart of his latest witch, but it's still there, deep in his gut, weakened and defenceless yet still fighting. It's a flicker of hope, a twinge of jealousy, an aching longing for something more, something real, something _true_.

But as much as he wants to be Sebastian Smythe, he knows his human half is merely a façade, a face to hide behind and a way to catch them off guard. He can lull them into a false sense of security with a charming smile, a tug on the lapels of his blazer, an easy, _"Hey there, killer."_ and a wink.

What they don't know is that the real killer is him, and they won't find out the truth until it's too late to save themselves.

This is just the way things are, the way they always have been, and the way Sebastian's so sure it always will be. He's so sure that nothing's ever going to change, that he's going to be stuck in this routine of _hunt, flirt, kill, hunt, flirt, kill_ for the rest of his miserable existence.

He's so soulless that he can't even bring himself to care.

_**I was born the day you loved me.**_

Everything changes when Sebastian is given the task of killing the Charmed Ones, the three most powerful witches in all of the world. He's told to target the youngest of the three brothers first, the_weakest_, the one that goes by the name of Dave Karofsky. The others are too strong and too wise, they'll see through him before he can even get a fireball in his hand, but Dave is naive and lost in his own head, quick to trust and believe, to_ love_.

He's also the one with the passive power, and that makes him the most defenceless, the easiest to beat if they ever had to fight. His eldest brother would quickly fling him across the room with a mere squint of his eyes, and the other wouldn't hesitate to blow him up with a flourish of his hands if he found out that Sebastian was planning on hurting them. But Dave can't do much with his power of premonition, not the way his brothers can.

So Sebastian targets him. At first, it's just like any other mission. The only difference is that this isn't some lowlife amateur demon or some pathetic mortal, or even a witch of a weaker status. As naive as this man may be, he's still one of the three most powerful beings in existence, one of the three brothers that Prophets and Seers have been raving about since time began. He has to be careful.

Still, it's easier than he thought, just as easy as any other target. Dave is smitten, easily wooed by Sebastian's confidence and charms. Sebastian can see him falling harder and harder each day, with each smile and each touch and every kiss he presses against those chapped lips.

Everything is going fine and he's so close to finally making a move, to doing what he came here to do, but that's when things change. He doesn't notice at first, the change happening slowly and steadily, and by the time he realises what's happening it's too late to stop it.

His human half is getting bigger, louder, stronger. It's no longer just a nuisance in the pit of his gut or a voice in the back of his head; it's taking over. It's fighting his demon half, becoming it's equal and trying to get control. It stops him from killing Dave, even when he has him distracted and he has an athame raised above his head. It makes him hunt another demon who dared to lay a hand on Dave, and torture him until his final squealing breath.

It makes _I'll kill them tonight_ turn into _I'll kill them tomorrow_. It makes tomorrow turn into a week, a fortnight, a month, until eventually he promises himself that he'll just _give it some time_.

It's suffocating and terrifying and for a while, Sebastian can't understand. He feels weaker, the anger and the dominance slowly fading as something else takes over. Something more, something real, something _true_ — everything he's been fighting since the day his mother convinced him to suppress his human half.

It's not until he's lying naked with Dave one night, the satin sheets draped lazily over their legs as he holds the boy in his arms, and Dave presses his lips to Sebastian's throat to whisper, _"I think I'm in love with you,"_ that he realises.

He's fallen in love with him, too.

All it takes is to hear those words leave Dave's mouth and it's like his demon half gives up, a surge of affection swelling in his chest instantly and making his human heart race with exhilaration. It's everything he's not supposed to feel, because he's a _demon_ and a demon can't _love_, but it's too late. He's fallen in love with the man he's supposed to kill and he doesn't know what to do.

He falls asleep cursing his mother for letting a human impregnate her all those years ago, for bringing him into the world and raising him in spite of the fact that his father's mortal blood runs through his veins.

_**And my love for you will keep me alive.**_

Loving Dave, Sebastian soon learns, must be what living in hell feels like. He's felt the pain of being vanquished more times than he can count, that burning sensation rippling through him from the inside out until he shatters into nothingness, only to find a way to piece himself back together again against all the odds.

He's felt the pain of heartbreak even more than that of being vanquished, and while he rarely lets it show, that leaves more scars than any potion or spell ever could.

But loving Dave is always what stops him from giving up, what encourages him to keep fighting, even when he's banished to the Demonic Wasteland and left for dead. It's a place that's not quite hell and not quite limbo, but somehow, somewhere in between. He's not dead and he's not alive, but there's no option of heaven in the Wasteland, and for average demons, there's no hope of ever escaping either.

Even Sebastian would've died instantly had he not been half human, and for the first time in his life, he finds himself blessing the mortal blood pumping through his body.

He spends months in there but it feels like years, familiarising himself with the monsters he has to face, learning how to steal powers from the other demons that end up there, always keeping Dave at the forefront of his mind as he dances with death every day.

By the time he escapes, he's more powerful than anyone could ever imagine, even as his human half remains strong within him. Dave's terrified of him, swearing to never love him or trust him again, calling him names that haunt him at night and damning him to hell.

Life doesn't feel like it's worth living when Sebastian finally accepts that he can't win Dave's trust back, but his love for Dave has made him invincible, all the power he's gained making him immortal. No matter how many spells and potions Dave and his brothers try, no matter how many demons Sebastian fights, no matter how many buildings he jumps off of or guillotine blades that slice his head away from his body, he's still alive, still fighting, still hopelessly hating his human half for loving Dave.

He dies, eventually, and even he can't understand why. Some sick twist of fate, a powerful new spell and a brand new potion that the brothers created, and he's gone. Fire ripples through him, pain fills every last fibre of his being, and that's the end of it. The last thing he sees is Dave's face crumpling when the man realises the vanquish actually worked, and he feels sickly satisfied at the knowledge that Dave never stopped loving him, even through all the bullshit.

Sebastian isn't _gone_, though. There's no Demonic Wasteland and no gates to hell, nor is there some greater power waiting in a big white chair to evaluate Sebastian's life. Instead there's a different kind of hell, a cosmic void between life and death where he's to spend the rest of eternity, forever trapped within the four walls of the Karofsky manor in a ghostal plane. He can see them, but they can't see him, and he knows that's the way it's always going to be — him always watching, Dave remaining none the wiser.

Years pass and time loses its concept as he watches Dave get injured over and over every time a new demon attacks, watches him fight and make potions and cast spells almost daily. Over time, he watches him bring home boyfriends and lovers, watches him fall in and out of love, getting hurt and hurting others, always bouncing back in the blink of an eye.

All Sebastian can do is watch and listen, unable to escape, unable to communicate, unable to do anything worthwhile. His human heart still aches deep in chest, his demonic side a whimper of its former self while Sebastian's love still burns so strongly.

He may be dead, but he's still living, his love for Dave keeping him chained and handcuffed to this astral plane. Part of him wonders if he'll move on when Dave dies, if the lack of his presence means his punishment is over and he'll get to pass on for real, but he doesn't get his hopes up.

He knows he's probably stuck here for all of eternity, destined to watch Dave's kids grow up, and his grandkids, and his great-grandkids, always knowing that these people were born because Sebastian was no longer around, always reminded that Dave managed to move on while he's forced to stay right where he is.

That's just the way it is, and the way it always will be.

_**Forever.**_

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_**FIN.**_  
**Feedback is appreciated.**


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